1. Field of the Invention
This invention relates to a sheet-material automatic feeding device which is used in an image forming apparatus, such as a facsimile, a printer, a copier or the like.
2. Description of the Related Art
In an image forming apparatus, such as a facsimile, a printer, a copier or the like, a sheet-material automatic feeding device, which individually separates and feeds sheets of a sheet material mounted on sheet-material mounting means, is used as means for feeding an original sheet material or a recording sheet material to an image reading unit or to an image forming unit.
In such a sheet-material automatic feeding device, a sheet material mounted on sheet-material mounting means is first fed by sheet-material prefeeding means to sheet-material separation/feeding means provided downstream. Sheets of the sheet material are individually separated by the sheet-material separation/feeding means. Each of the separated sheets is fed to sheet-material conveying means provided downstream of the sheet-material separation/feeding means, and is further fed by the sheet-material conveying means to an image reading unit or to an image forming unit.
Accordingly, in the sheet-material automatic feeding device, the sheet material must be mounted on the sheet-material mounting means at such a position that it can be prefed by the sheet-material prefeeding means.
The sheet material mounted on the sheet-material mounting means can be prefed by the sheet-material prefeeding means when the leading end of the sheet material is positioned between a position where it passes through the sheet-material prefeeding means and a position immediately upstream of the sheet-material separation/feeding means.
Therefore, in a conventional sheet-material automatic feeding device, the following approaches are, for example, adopted in order that a sheet material mounted on sheet-material mounting means can be securely prefed by sheet-material prefeeding means.
(1) The user is directed by an instruction manual or the like to mount the sheet material on sheet-material mounting means so that the leading end of the sheet material contacts a nip portion of sheet-material separation/feeding means (a first conventional approach).
(2) The position for placement of the trailing end of each sheet material is indicated on the sheet-material mounting means, so that a sheet material is mounted on the sheet-material mounting means while aligning its trailing end with the indicated position (a second conventional approach).
(3) An openable/closable shutter is provided on a conveying path between the sheet-material prefeeding means and sheet-material separation/feeding means. When the leading end of the sheet material contacts the shutter, the sheet material is mounted on the sheet-material mounting means (a third conventional approach).
In the above-described first conventional approach, if the leading end of the sheet material contacts the nip portion of the sheet-material separation/feeding means with a force equal to or greater than a predetermined pressing force, the leading end of the sheet material will sometimes pass through the nip portion. If the sheet material is fed under such circumstances, two or more sheets of the sheet material are in some cases simultaneously fed.
In the second conventional approach, the operation of aligning the rear end of the sheet material with the indicated position on the sheet-material mounting means is troublesome when the sheet material comprises a large amount of sheets. Furthermore, this approach is useless when the size of the sheet material is not one of the predetermined formats, causing the same problem as in the first conventional approach.
In the third conventional approach, since the shutter is openably and closably driven by an actuator, such as an electromagnetic solenoid or the like, the cost of the sheet-material automatic feeding device increases.